Pump apparatus for pumping melt metal

ABSTRACT

Molten metal is pumped from a furnace to a place where it is utilized using a gas-plunger pump having a container holding the chamber with an inlet for drawing metal from the furnace to the chamber, and with an outlet for forcing metal out of the chamber to the place of use. The inlet and outlet are disposed at the bottom of the chamber. A suction and pressure system includes a closed circuit containing a vacuum tank, a pressure tank, a vacuum pump/compressor unit connected between them, and a first valve. The closed circuit is connected to the chamber via a conduit. A control system alternately connects and disconnects the vacuum tank and pressure tank and substantially synchronously alternately opens and closes the inlet and outlet by actuation of valves associated with the inlet and outlet.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a pump apparatus for pumping melt metalfrom a furnace to a place where it is to be used, said pump apparatuscomprising a pump of gas-plunger type having a container holding achamber with an inlet for drawing molten metal from the furnace to thechamber via a suction pipe immersed in the furnace melt, and with anoutlet for forcing molten metal out of the chamber to the place of use;a gas-operated suction and pressure system comprising a suction sourcewith a vacuum pump, a pressure source with a compressor and a conduitprovided with valve means for alternately connecting and disconnectingthe suction and pressure sources, the gas pressure of the latter actingdirectly on the melt in the chamber inside the container; and a controlsystem for controlling the pump apparatus, said container beingvertically aligned and arranged immediately above and in line with thefurnace, said outlet being arranged at the bottom of the container.

It is known through patent specifications EP-190 680, U.S. Pat. No.4,010,876, DE-1 197 591, GB-1 596 826, U.S. Pat. No. 4,708,191, FR-2 061708, DE-3 923 079 and JP-1 095 856, for instance, to keep componentsthat are in contact with the melt heated, to protect the melt with aninert gas, to measure the level of the melt inductively or capacitively,and to use graphite of ceramic material for certain components that arein contact with the melt.

Each of the known pump apparatus is limited to its own specific castingprocess and, if they are of the pressure-increasing type the mechanicaldesigns are so complex that they reduce operating reliability andservice life.

The object of the present invention is to achieve an improved pumpapparatus that is relatively simple in design, reliable in operation,pressure-increasing, has long service life and can be used for all usualcasting methods and metals.

The pump apparatus proposed according to the invention is substantiallycharacterized in that the inlet of the container is arranged at thebottom thereof; that valve means are arranged inside the container toalternately open and close said inlet and outlet; that the suction andpressure system comprises a closed circuit containing a vacuum tank, apressure tank, a vacuum pump/compressor unit connected therebetween, andsaid valve means, and is connected to the chamber in the container viasaid conduit; and that said control system is arranged to alternatelyconnect and disconnect the vacuum tank and pressure tank and tosynchronously or substantially synchronously therewith alternately openand close said inlet and outlet.

The pump apparatus according to the invention offers several valuableadvantages over conventional pump apparatus:

The entire pump is located above the melt. Only parts of the suctionpipe and filter are located in the melt.

The pump is pressure-increasing up to substantially the pressureprovided by the vacuum pump/compressor unit. This improves the qualityof the castings and increases productivity. Conventional systems forlow-pressure casting produce approximately 1 bar.

Thanks to a specific level-measuring system the level of the melt can bemeasured without any instrument coming into contact with the melt, andextremely accurate dosing is possible.

A closed pipe system is used, thereby reducing oxidation of the moltenmetal.

Simpler holding furnaces can be used.

The working environment is improved since no open vessels containingmelt need to be transported.

All parts of the pump apparatus according to the invention that comeinto contact with the melt are manufactured out of ceramic material,which is resistant to the melt (aluminium, for instance, is extremelyaggressive to most materials) and withstands the temperature. All partscoming into contact with the melt are also surrounded by furnace modulesand are thus heated. This prevents any "freezing" in pipes and pump.Like the factory furnaces, the pumps are heated during production stopsand over weekends.

The pumping action is thus obtained by means of a gas-operatedsuction-pressure system. A vacuum pump/compressor unit is locatedbetween a vacuum tank and a pressure tank, this unit ensuring that thegas is evacuated in the vacuum tank and that a sufficiently highpressure prevails in the pressure tank. A valve effects the necessaryswitching between drawing up and forcing out the metal. Since the gaswithdrawn from the pump is hot, it passes an accumulator where it emitsenergy. Similarly, the pressure-generating gas passes the accumulatorand receives additional energy. This enables energy consumption to be aslow as possible. The gas used is inert.

A system for lifting and possibly turning the pump valves is provided inorder to regulate inflow and outflow of molten metal to the pump. Testsindicate that raising valves is to be preferred. The movement can ofcourse be achieved using various types of drive sources.

The entire pump cycle is monitored by a control system, preferably aPLC. The advantage of the system is that flow and pressure arecontrolled throughout the cycle.

Thanks to the pump apparatus according to the invention being given thefeatures described in claim 1 it can be used for all types of castingmethods. It can therefore be connected to a place of use arranged, forinstance, for casting melt in a mould, for dosing melt into a containerin a die-casting machine, for dosing melt into a chill or sand form orfor supplying melt through a die equipment of any desired profile.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described further in the following with referenceto the drawings.

FIG. 1 is a side view of a furnace and a pump apparatus mounted thereonand having control system and gas-operated suction and pressure system.

FIG. 2 is longitudinal section through the pump apparatus according toFIG. 1 but with said two systems omitted.

FIG. 3 shows cross-sectional views of the bottom part of the pump in thepump apparatus shown in FIG. 2 and show a valve cone and itsco-operation with the valve seat in the bottom plate, and connection ofthe suction pipe.

FIG. 4 is a longitudinal section through a part of the pipe connectionbetween pump and place of use.

FIG. 5 is a longitudinal section through an interceptor at the outer endof the connection from the pump.

FIG. 6 shows longitudinal sections through two different embodiments ofthe suspension of the pump container.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to FIGS. 1 and 2 it is shown schematically therein a pumpapparatus for liquid metal, comprising a pump 1 having a container witha chamber 18 to receive melt 4. The width or diameter of the chamber 18is small in relation to its height, e.g. about 1:14-1:7, preferably 1:5.A ceramic filter 3 is mounted at the inlet to the suction pipe 2 of thepump 1, in order to remove any impurities in the melt 4, the melt beingenclosed in gas-tight condition in a furnace 5. This filter 3 must bereplaced at regular intervals. When replacing the filter the entire pump1 is lifted up out of the furnace 5 and the replacement is facilitatedsince the filter holder 6 is kept in place by a quick connection.

The suction pipe 2 is made of ceramic material. An edge on the suctionpipe allows it to be pressed against a support plate 7, see FIG. 3.Dampening insulation 8 is placed between the pipe 2 and plate 7 toprevent chipping of the edge. The joint between the suction pipe 2 and ablock 9 must be gas-tight. This can be achieved by both contact surfacesbeing lapped to provide sufficient adhesion for the sealing function,compare gauge block system, or by using seals. Extra abutment is alsoeffected using a spring system 10. A graphite seal 11 is used sinceconventional seals are not resistant to aluminium. However, graphitebecomes oxidized at high temperatures and a compressible seal 12 istherefore placed outside the graphite seal 11 to prevent oxidation. Thegraphite seal 11 seals against the melt and the outer, conventional seal12 protects the graphite seal 11 from oxygen in the air.

The block 9 is made of ceramic material with valve seats for therod-shaped valve cones 13. The valve seat is preferably conical to avoidchipping of the ceramic and to better fit the spherical form of thevalve cones 13, see FIG. 3. Since the valve cones 13 also come intocontact with the melt, these are made of ceramic material. The cones 13are guided by graphite bushing 14 and are attached in metallic holders15 which are in turn secured to the lifting and turning devices 16 and17, respectively. The lower ends of the cones 13 are spherical tocompensate unintentional inclination.

It has been found that impurities in the melt adhere more easily to thepump components at high flow rates, and the cones 13 therefore open agap between themselves and the block 9 before evacuation or build-up ofpressure has occurred in the chamber 18 in the container, see FIG. 3.The control system 19 then balances the fluid pressure and gas pressureso that no flow occurs. Evacuation or pressure build-up in the chamber18 in the container occurs when the gap is at its largest.

Since impurities may adhere to the material in the block 9 and cones 13despite the measures described above, the cones 13 are turned at regularintervals so that they are ground against the valve seat in the block 9.Turning is achieved by means of turning devices 17.

The container holding the chamber 18 is also made of ceramic materialand hold the melt to be dosed out to the user. It must therefore begas-tight to both the block 9 and an upper container flange 20. The sealagainst the block 9 is in principle the same as the one describedearlier for the suction pipe 2. A conventional seal 21 may be used forthe container flange 20 since this does not come into contact with themelt.

A helical groove is provided in the lower part of the container whichencloses the chamber 18. A metal wire 22 is placed in this groove sothat a solenoid is achieved. By allowing a high-frequency current topass through the solenoid, a specific inductance is obtained. When themetal flows into the chamber 18 inside the container, the inductancealters depending on the level of the metal. The level can be establishedby feeding these signals into the control system 19 included in the pumpapparatus. The starting position is always the maximum level. To preventoverfilling the chamber 18 in the container an electrode 23 acting as asafety breaker, is installed in the container. With the aid of othersignals to and from the place of use and the pump 1, the system 19 isable to control the casting process with respect to both the flow andpressure.

The container holding the chamber 18 is surrounded by a furnace 24 whichprovides the desired temperature.

In order to avoid radiation heat on the container flange 20, aninsulation 25 is placed between the melt surface 26 and the containerflange 20. The insulation is suspended on shoulders (not shown) in thechamber 18 and permits the passage of gas in both directions.

The outlet pipe has parts 27 surrounded by furnace modules 28, see FIG.4. The parts 27 of the outlet pipe and the furnace modules 28 aresupported by outer metal pipes 29 acting as supporting elements up tothe place of use. Seals 31 are mounted between the parts 27 of theoutlet pipe and the parts 27 are joined with the aid of jointing sleeves30. Since pressure build-up will occur in the outlet pipe 27, thesealing is substantially the same as that described previously for thesuction pipe 2. That being so, a graphite seal 32 is added.

An interceptor 33 is mounted at the end of the outlet pipe 27, see FIG.5. The interceptor 33 acts to automatically maintain the melt level andalso as a protective seal against oxygen. As additional protectionagainst the formation of metal oxides, an automatic spray device 34 foroxide-solving chemicals may be installed above the interceptor 33.

Either a suspended pipe 35 or a bottom flange 37 in combination withconnecting rods 36 is used to keep the various parts of the pumptogether, see FIG. 6. Clamping is obtained by tensioning the containerholding the chamber 18 and block 9, between the container flange 20 andsuspended pipe 35 (FIG. 6, upper picture) or the bottom flange 37 (FIG.6, lower picture). To eliminate problems with the different coefficientsof linear expansion in the various materials, the package is clampedwith the aid of said spring system 10.

The pump 1 can be designated a gas-plunger pump operating with an inertgas as plunger. At evacuation of the container volume, the valve cone 13opens at the inlet 38 and the melt rises in the chamber 18 inside thecontainer. When molten metal is required at the place of use, the valvecone 13 opens at the outlet 39 and gas forces the melt out until thepredetermined volume has been obtained.

The pump apparatus also includes a suction and pressure system 40comprising a closed circuit 49 including a vacuum pump/compressor unit41, a vacuum tank 42, a pressure tank 43 and a valve 44, the circuit 40being connected via said valve 44 to the chamber 18 in the container bya conduit 50 containing a heat accumulator 45. The system 40 is thusentirely closed and no gas is therefore consumed. The vacuumpump/compressor unit 41 operates continuously, transporting gas from thevacuum tank 42 to the pressure tank 43. Upon evacuation, the valve 44opens the communication between the chamber 18 in the container and thevacuum tank 42. When the melt is forced out, the valve 44 opens thecommunication between the chamber 18 and the pressure tank 43. To ensureminimum energy loss, the gas emits thermal energy to the heataccumulator 45 at evacuation and extracts energy from this accumulator45 when pressing out melt.

The whole casting and dosing process is monitored by the control system19 in such a way that flow and pressure are regulated and controlledthroughout the casting process.

I claim:
 1. A pump apparatus for pumping molten metal from a furnace toa place where it is to be used, comprising: a gas-plunger pump having acontainer holding a chamber with an inlet for drawing molten metal fromthe furnace to the chamber via a suction pipe immersed in the furnacemelt, and with an outlet for forcing molten metal out of the chamber tothe place of use; a gas-operated suction and pressure system comprisinga suction source with a vacuum pump, a pressure source with a compressorand a conduit providing with first valve means for alternatelyconnecting and disconnecting the suction and pressure sources, the gaspressure of the latter acting directly on the melt in the chamber insidethe container; a control system for controlling the pump apparatus; saidcontainer being vertically aligned and disposed immediately above and inline with the furnace, said outlet being disposed at the bottom of thecontainer; said inlet of said container is disposed at the bottom ofsaid container; wherein said suction and pressure system comprises aclosed circuit containing a vacuum tank, a pressure tank, a vacuumpump/compressor unit connected therebetween, and said first valve means,and is connected to the chamber in the container via said conduit; andwherein that said control system is disposed to alternately connect anddisconnect the vacuum tank and pressure tank and to substantiallysynchronously therewith alternately open and close said inlet andoutlet.
 2. A pump apparatus as claimed in claim 1, wherein a heataccumulator 45 is arranged in the conduit 50 connecting said circuit 49to the chamber 18 in the container, in order to store thermal energyfrom the gas flowing out of the chamber 18 and emit thermal energy tothe gas flowing into the chamber
 18. 3. A pump apparatus as claimed inclaim 1, wherein the valve means inside the chamber 18 in the containerconsist of vertical valve cones 13 of ceramic material, each connectedto a lifting device mounted outside the pump 1 for raising and loweringthe valve cone 13 in relation to the valve seat of the inlet 47 andoutlet 48, respectively, and that the valve cones 13 and valve seatshave cooperating spherical and/or conical sealing surfaces.
 4. A pumpapparatus as claimed in claim 3, wherein the valve cones 13 arepivotably journalled by means of a turning device 17 to effect grindingof the sealing surfaces in order to remove impurities that adherethereon from the melt.
 5. A pump apparatus as claimed in any of claim 1,wherein the control system 19 is arranged to control the valve means 44in the circuit 49 and the valve means 13 within the chamber 18 so that,before a suction or pressure phase is commenced, the pressure isbalanced and the relevant valve means 13 is partially opened in order tominimize the flow rate of the melt into or out of the chamber
 18. 6. Apump apparatus as claimed in any of claim 1, wherein a metal wire 22 ismounted in or on the outer side of the wall of the container holding thechamber 18, in order to form a solenoid in a current circuit, theinductance of the solenoid constituting a value indicating the level ofthe melt in the chamber
 18. 7. A pump apparatus as claimed in any ofclaim 1, wherein the facing sealing surfaces of every joint between twocomponents of the pump apparatus that come into contact with melt aresealed both by a conventional external seal 31 which will withstand hightemperatures, as a protection against oxygen, and also a graphite seal32 as a protection against the melt.
 8. A pump apparatus as claimed inany of claim 1, wherein an interceptor 33 is arranged at the end of theconnection 27 between the container holding the chamber 18 and the placeof use.
 9. A pump apparatus as claimed in claim 8, wherein a spraydevice 34 is arranged in conjunction with the interceptor 33 for thesupply of chemicals to dissolve oxides.
 10. A pump apparatus as claimedin any of claim 1, wherein a ceramic filter 3 is arranged in the end ofthe suction pipe 2 immersed in the melt and is arranged to be replacedby raising the pump 1 together with the suction pipe.
 11. A pumpapparatus as claimed in any of claim 1, wherein an insulating body 25 isarranged in the upper part of the container holding the chamber 18closed by a container flange 21, said insulating body 25 forming aprotection against radiation from the melt located below the insulatingbody
 25. 12. A pump apparatus as claimed in any of claim 1, wherein thecontainer holding the chamber 18, and the block-shaped bottom 9 of thecontainer are spring-clamped between an upper container flange 20 andeither a suspended pipe 35 or a bottom flange 37 in combination withconnecting rods 36 spring-clamped by means of spring devices 10 at thecontainer flange
 20. 13. A pump apparatus as claimed in any of claim 1,wherein the control system 19 is arranged at regular intervals to openthe valve means 13 in the inlet 47 from the suction pipe 2 andsimultaneously connect the pressure tank 43 in order for the gas toforce the melt back through the suction pipe 2 and through a filter 3arranged at its lower end, thereby cleansing it from particles.
 14. Apump of a gas-plunger type for pumping molten metal, comprising:achamber having an inlet, a suction pipe connected to the inlet, and anoutlet, said outlet being provided adjacent the bottom of said chamberand said inlet also being disposed adjacent the bottom of said chamber;a gas operated suction and pressure system having suction and pressuresources, and comprising: a conduit with a first valve for alternatelyconnecting and disconnecting the suction and pressure sources, saidconduit connected to said chamber; a vacuum tank; a pressure tank; and avacuum pump/compressor connected between said vacuum tank and saidpressure tank; a second valve disposed inside said chamber toalternately open and close said inlet and outlet; and control means foralternately connecting and disconnecting said vacuum tank and pressuretank and to substantially synchronously therewith alternately open andclose said second valve to open and close said inlet and outlet. 15.Apparatus as recited in claim 14 wherein said control means comprisesmeans for controlling said first and second valves so that before asuction or pressure phase is commenced the pressure is balanced and saidsecond valve is partially opened in order to minimize the flow rate ofmolten metal into or out of said chamber.
 16. Apparatus as recited inclaim 14 further comprising a heat accumulator disposed in said conduitfor storing thermal energy from gas flowing out of said chamber, and forsupplying thermal energy to gas flowing into said chamber.
 17. Apparatusas recited in claim 14 wherein said second valve comprises a pluralityof vertically disposed valve cones of ceramic material each connected toa lifting device disposed outside of said pump for raising and loweringsaid valve cone with respect to a valve seat defining said inlet oroutlet, respectively, said valve cones and valve seats havingcooperating spherical or conical sealing surfaces.
 18. Apparatus asrecited in claim 14 further comprising an interceptor connected to saidchamber, and a spray device for supplying chemicals, to dissolve oxides,to said interceptor.
 19. Apparatus as recited in claim 14 wherein saidcontrol means further comprise means for opening said second valve atsaid inlet and simultaneously connecting said pressure tank to saidchamber so that gas from said pressure tank forces molten metal out ofsaid suction pipe; and further comprising a filter disposed at an end ofsaid suction pipe remote from said chamber, said control means forcingmolten metal through said filter to clean particles therefrom. 20.Apparatus as recited in claim 14 further comprising a block shapedbottom portion defining said chamber and operatively spring clamped toan upper flange also defining said chamber.